1. Field of the Invention
The present invention is related to a method of making a low-profile wire connection for stacked dies and more particularly to the method of wire connection for an upper die arranged with two wires bent around a second bonding pad.
2. Description of the Related Art
The conventional method of making a wire connection includes a wire electrically connecting a first bonding pad and a second bonding pad to form a closed loop in a semiconductor device. The wire extends upward from the first bonding pad and downward to the second bonding pad, so that the wire has a high profile between the first bonding pad and the second bonding pad. Because the high profile is mechanically supported only at the point of the bonding pad, the high profile can easily be shifted by stress. When the semiconductor device is in the molding process, the liquified encapsulant material pushes the wires, which can easily be shifted, and then wire sweeping occurs. To overcome the above-mentioned wire sweep problem, the wire is bent to decrease the height of the wire and to increase the strength of structure.
U.S. Pat. No. 5,156,323, issued on Oct. 20, 1992 to Kumazawa et al., discloses a wire bonding method. As shown in FIG. 1, a capillary 100 mechanically bonds wire 110 to the first bonding pad 101 and is moved upward a first distance 111. As shown in FIG. 2, the capillary 100 is then moved away from the second bonding pad to form a first bent portion 112 thus making the first reverse action to bend the wire 110 at en appropriate angle. As shown in FIG. 3, the capillary 100 is again raised an appropriate length to form a second distance 113. As shown in FIG. 4, wire 110 is bent at an appropriate angle to form a second bent portion 114, so that the capillary 100 is moved away from the second bonding pad. As shown in FIG. 5, the capillary 100 is further raised and then aimed toward the second bonding pad through a third distance 115 by feeding out the wire 110 to a length which is sufficient to make a wire loop. As shown in FIG. 6, the capillary 100 is moved down to the second bonding pad 102 according to the trace where bonding is performed. The wire 110 has the first bent portion 112 and the second bent portion 114 which reduce the height of wire and increase its strength.
Although the wire bonding method of U.S. Pat. No. 5,156,323 has the first bent portion and the second portion to reduce the height and increase the strength of the wire, this wire bonding method cannot be adapted for use in a stacked dies structure. if the stacked dies stucture uses this wire bonding method, the wire of the lower die and the wire of the upper die are in too close proximity on the second bonding pad causing cross talk. Additionally, the length of the upper wire renders it too long and weak, and it is shifted by the encapsulant material causing it to touch the other wire during compound molding.
The present invention intends to provide a wire bonding method which has a bent portion of upper wire at the second bonding point to reduce the height and increase the strength of the wire in such a way as to mitigate and overcome the above problem.